1. Field of the Invention
The present invention relates to a coil component such as an inductor or other coil component, and a method of producing the same, and more particularly, the present invention relates to a lamination-type coil component including a lamination-type coil included in an element such as a lamination-type inductor, and a method of producing the same.
2. Description of the Related Art
A lamination-type inductor is a typical lamination-type coil component. For example, as shown in FIGS. 6A and 6B, the lamination-type inductor has a structure in which a lamination type coil 52 (FIG. 6B) including a plurality of internal conductors defining coil patterns 52a (FIG. 6B) connected together is disposed in an element in the form of a chip element 51, and moreover, external electrodes 53a and 53b (FIG. 6A) are arranged so as to be connected to both ends of the coil 52, respectively.
Such a lamination type inductor is produced, for example, by laminating a plurality of magnetic green sheets 54, each having a coil pattern 52a provided on the surface thereof, via a printing method, laminating magnetic green sheets (sheets defining outer layers) 54a each having no pattern provided thereon to the upper portion and the lower portion of the stack of laminated magnetic green sheets 54, press-bonding the sheets, connecting the respective coil patterns 52a through via-holes 55 to define a coil 52, as shown in FIG. 6B, firing the laminate (an unfired body), providing conductive paste on both end portions of the body 51, and firing to form external electrodes 53a and 53b (FIG. 6A).
In the conventional lamination-type inductor as shown in FIG. 7, the magnetic green sheets 54 each have a coil pattern 52a printed or provided on the surface thereof, so that the pattern 52a and its surrounding have a difference in height (that is, the portion of the green sheet 54 where the coil pattern 52a is printed is thick, while the portion thereof where no coil pattern is printed is thin). Therefore, the lamination and press-bonding of the plurality of magnetic green sheets 54 cannot be evenly pressed to be bonded together. Thus, in the conventional lamination-type inductor, the electrical characteristics become uneven, delamination occurs, and further problems arise. Further, an air layer may be formed between layers. This causes the problem that distributed capacitances are produced between the respective coil patterns 52a of the layers, due to the air layers, and the initial electrical characteristics and those after repeated use become different. Therefore, the electrical characteristics are unstable.
To solve the problems discussed above, a method of producing a lamination-type inductor has been proposed (Japanese Examined Patent Application Publication No. 7-123091), in which an auxiliary magnetic layer 56 is provided around the coil pattern 52a printed on the surface of each magnetic green sheet 54 in such a manner that the thickness of the auxiliary magnetic layer 56 is greater than that of the coil pattern 52a, after firing, as shown in FIGS. 8 and 9.
In the case of the lamination-type inductor produced by this method, a gap is formed between the coil pattern 52a and the magnetic layer 54 adjacent to the coil pattern 52a in the thickness direction (the sintered layer of the magnetic green sheet). Due to the gap 57 having a relative dielectric constant lower than that of the magnetic layer 54, the distributed capacitances are reduced, and the loss at a high frequency is decreased. Moreover, variations in the electrical characteristics, caused by repeated use, are suppressed.
However, in the case where the auxiliary magnetic layer is thicker than the coil pattern as in the above-described lamination-type inductor, the connection state of the coil patterns on the respective magnetic green sheets connected together through a via-hole becomes unstable, the stability of direct current resistance is insufficient, and the reliability is deteriorated.
To overcome the problems described above, preferred embodiments of the present invention provide a method of producing a lamination-type coil component in which coil patterns provided on each of magnetic green sheets are securely connected to each other through via-holes to form a coil pattern, the direct current resistance is very low, and the stability is excellent with high reliability.
According to a first preferred embodiment of the present invention, a method of producing a lamination type coil component includes the steps of applying an electrode material for formation of a coil to a magnetic green sheet having a via-hole formed therein in an area including the via-hole, arranging the electrode material into a predetermined pattern whereby a coil pattern is formed with the electrode material being filled into the via-hole, providing a magnetic material layer having a thickness which is less than the coil pattern so as to surround the coil pattern, laminating a plurality of magnetic green sheets having the coil pattern and the magnetic material layer provided thereon, whereby a laminate having a coil provided inside thereof is formed, press-bonding the laminate, and heat treating the press-bonded laminate.
By applying an electrode material to form a coil on a magnetic green sheet having a via-hole provided therein in an area including the via-hole, into a predetermined pattern, whereby a coil pattern is formed with the electrode material being filled into the via-hole, arranging a magnetic material layer having a thickness which is less than the coil pattern so as to surround the coil pattern, plural magnetic green sheets containing the magnetic green sheets each having the coil pattern and the magnetic material layer formed thereon are laminated, and the laminate is press-bonded, the thickness of the electrode material in the area where the via-hole is formed as viewed in the plan view is thicker than the magnetic material layer in an area surrounding the magnetic material layer. Thereby, in the press-bonding step, a sufficient pressure is applied to the electrode material constituting the coil pattern and the electrode material in the via-hole. Thus, the coil patterns formed on the respective magnetic green sheets can be securely connected through the via-hole. A lamination-type coil component having very low direct current resistance, excellent stability, and very high reliability is achieved.
In the present invention, the statement that xe2x80x9cthe magnetic material layer having a thickness which is less than the coil pattern is formed in an area surrounding the coil patternxe2x80x9d means that the sum of the thickness of the electrode material in the via-hole and the thickness of the electrode material constituting the coil pattern is greater than the sum of the thickness of the magnetic green sheet and the thickness of the magnetic material layer in an area surrounding the electrode materials. Accordingly, in the method of producing a lamination type coil component according to preferred embodiments of the present invention, the sum of the thickness of the electrode material in the via-hole and the thickness of the electrode material constituting the coil pattern is greater than the sum of the thickness of the magnetic green sheet and the thickness of the magnetic material layer in the area surrounding the electrode materials.
As a result, in the press-bonding step, the electrode material constituting the coil pattern and the electrode material in the via-hole is sufficiently pressed, and the coil patterns provided on the respective magnetic green sheets are securely connected to each other through the via-hole.
The coil pattern and the magnetic material layer can be formed by different methods. As an example, screen printing, plating, photolithography, or other suitable methods can be used.
Preferably, at least one of the thicknesses of the coil pattern and the magnetic material layer provided on each magnetic green sheet and the thickness-reduction ratios of the coil pattern and the magnetic material layer in the press-bonding step are controlled. Thereby, after the press-bonding, the sum of the thickness of the electrode material in the via-hole and the thickness of the coil pattern is greater than the sum of the thickness of the magnetic green sheet and the thickness of the magnetic material layer.
By controlling at least one of the thicknesses of the coil pattern and the magnetic material layer provided on the magnetic green sheet and the thickness-reduction ratios of the coil pattern and the magnetic material layer in the press-bonding step, the sum of the thickness of the electrode material in the via-hole and the thickness of the coil pattern are preferably greater than the sum of the thickness of the magnetic green sheet and the thickness of the magnetic material layer after the press-bonding. The respective coil patterns are securely connected to each other through the via-hole. Thus, a lamination-type coil component having very low direct current resistance, excellent stability, and very high reliability is achieved.
More specifically, at least one of the shrinkage ratio of the coil pattern provided on the magnetic green sheet in the heat treatment step, and the shrinkage ratio of the magnetic material layer arranged so as to surround the coil pattern is controlled. Thereby the sum of the thickness of the electrode material in the via-hole and the thickness of the coil pattern is greater than the sum of the thickness of the magnetic green sheet and the thickness of the magnetic material layer after sintering.
By controlling at least one of the shrinkage ratio of the electrode material (containing the electrode material filled in the via-hole) constituting the pattern provided on the magnetic green sheet in the heat treatment step (sintering process), and the shrinkage ratio of the magnetic material layer arranged so as to surround the coil pattern (the electrode material layer) in the heat treatment step (sintering process), the sum of the thickness of the electrode material in the via-hole and the thickness of the coil pattern after the sintering is greater than the thickness of the sintered magnetic body obtained by sintering the magnetic green sheet and the magnetic material layer. The respective coil patterns are securely connected to each other through the via-hole. A lamination-type coil component having very low direct current resistance, excellent stability, and very high reliability is achieved.
Still more specifically, the lamination-type coil component may be an inductor or other electronic component.
The present invention can be applied to methods of producing components provided with different types of lamination-type coils. By utilizing the present invention as a method of producing an inductor, a lamination-type inductor having a high reliability is efficiently produced.
According to a second preferred embodiment of the present invention, a lamination-type coil component is provided in which a lamination-type coil is arranged in a sintered magnetic body, which includes magnetic layers each having a coil conductor provided on a sintered magnetic layer and a sintered magnetic material layer arranged so as to surround the coil conductor, the coil conductors being connected to each other through the electrode material in via-holes, the sum of the thickness of the electrode material in the via-holes and the thickness of the coil conductor is greater than the sum of the sintered magnetic layer and the sintered magnetic material layer.
By setting the sum of the thickness of the electrode material in the via-holes and the thickness of the coil conductor to be greater than the sum of the sintered magnetic layer and the sintered magnetic material layer, the respective coil conductors are securely connected to each other. A lamination-type coil component having high reliability is achieved.
The lamination-type coil component can be efficiently produced by any one of the above-described methods.
Preferably, the lamination type coil component is an inductor but may also comprise other types of electronic components.
The present invention can be applied to components provided with different lamination-type coils. By applying the present invention to an inductor, a lamination-type inductor having high reliability is provided.
Other features, characteristics, elements and advantages of the present invention will become apparent from the following description of preferred embodiments thereof with reference to the attached drawings.